1. Field of the Invention
The present invention relates to a magnetic head and more particularly to a magnetic head including a magnetic core at least a portion of which is constructed by a magnetic then film.
2. Description of the Prior Art
Recently, there has been an increasing demand for magnetic head including a magnetic thin film as a core material, especially magnetic heads having a magnetic core which is formed by a thin film formation technique to a trend that higher recording density is employed in magnetic recording. The above magnetic head hereinafter. Particularly, thin film magnetic heads have already been put on the market for computer external recording units, still video recorders, and the like.
A method usually used for fabricating a thin film head will be explained below. At first, a magnetic material such as Sendust, Permalloy or the like is deposited on a surface of a substrate to form a lower magnetic layer, and then an insulation layer composed of SiO.sub.2 or the like is deposited thereon. Subsequently, an electroconductive layer composed of Al or Cu is formed on the insulation layer.
After depositing again an insulation layer composed of SiO.sub.2 on the electroconductive layer, magnetic contact holes and a magnetic gap are formed by a photolithographic etching in the second insulation layer. Then, an upper magnetic layer composed of Sendust or the like is deposited on the insulation layer and is formed to have a predetermined shape.
Next, after forming a protective layer or bonding a protective plate on the upper magnetic layer in order to protect the element portion of the resulting chips, the chips are each cut to form a sliding face to complete thin film magnetic head chips.
It is required that the material of the substrate used in the thin magnetic film head thus constructed satisfy the following characteristics and requirements.
(1) The material of the substrate has a coefficient of thermal expansion which approximates the coefficient of thermal expansion of the metallic magnetic material. Mismatching of the coefficient of thermal expansion between the two materials causes the peeling-off of the layers, the deterioration of the magnetic characteristics upon increase in stress, or the curling of the substrate.
(2) The substrate has a small void volume, and its surface is processed to give a mirror surface smooth enough to give substantially no adverse influence on the growth of films.
(3) The substrate has a good processability and scarcely cause failures or cutouts such as chipping upon cutting.
(4) The substrate has a good resistance to abrasion upon the sliding between the substrate and a magnetic recording medium, thus causing no non-uniform abrasion and giving no damage on the magnetic recording medium.
(5) The substrate is available at low cost.
In order to meet the above-described requirements, ferrites and ceramics have heretofore been used as a raw material for the manufacture of substrates, and the substrates composed of such materials are highly reliable. In addition, attention has recently been paid on crystallized glass, which is easy to control its coefficient of thermal expansion and hardness or its particle diameter of crystal grains when manufacturing substrates therefrom.
The substrates manufactured using crystallized glass have a coefficient of thermal expansion larger than that of the substrates made of a ferrite, and therefore it is easier to match the substrates with metallic cores made of a metal or alloy such as Sendust with respect to the coefficient of thermal expansion as compared with the substrates made of a ferrite. Crystallized glass includes crystal grains which are smaller than those of ceramics, so that there seldom occurs chipping upon the processing thereof, or dropping of crystal grains or non-uniform abrasion of crystal grains upon the sliding with magnetic recording media. Furthermore, crystallized glass enables the manufacture of substrates with apertures much larger than those made of ferrites or ceramics, and therefore they are advantageous in reducing cost of head by mass production.
While the substrates made of crystallized glass have various advantages as described above, they have rarely been used practically in actual commercial products because of their low reliability upon the sliding with magnetic recording media. Conventional substrates made of crystallized glass suffer from high abrasion rate, which causes the cohesion of powder formed as a result of abrasion on the substrates. Conversely, the use of substrates made of crystallized glass which is hard and small in abrasion wear causes a problem of non-uniform abrasion that the space between the head gap and the magnetic recording medium increases because the abrasion rate of the magnetic core is higher than that of the substrate. In addition, because the substrate made of crystallized glass is hard, the magnetic recording medium is likely to be damaged.